1. Field of the Invention
The present invention relates in general to a method for forming a longitudinal fiber web, wherein substantially mutually parallel synthetic fibers are embedded in a carrier matrix, also of synthetic material, wherein the longitudinal direction of the fibers is directed parallel to the longitudinal direction of the web.
More particularly, the present invention relates to a method for forming such a web in a continuous process, whereby the length of that web may in principle be infinitely large; such a web will hereinafter be indicated by the phrase “continuous” web.
2. Description of the Prior Art
Manufacturing a longitudinal fiber web in a continuous process is known per se. By way of example, reference is made to the Dutch patent 1014995 and the International patent application PCT/NL01/00316 (WO01/083345), of which publications the full content is incorporated here by reference. Basically, this means that a fiber bundle is applied to or embedded in a carrier layer of a material with a lower flow temperature. The structure thus formed is subjected to a thermal treatment, usually with the use of thermal rollers, wherein the combination of carrier layer and fibers is heated to a well-controlled temperature in a temperature range which is chosen such that the carrier layer will flow but the fiber bundle will not. A good adhesion between the fibers and the liquid carrier material comes into being. In the embodiment of the said publications where the fibers are embedded between two carrier layers, after cooling down, the two carrier layers are melted together to a whole that is indicated as carrier matrix. The product formed is subsequently wound on a roll.
It is possible to make a transverse fiber web out of such a longitudinal fiber web by cutting pieces of the longitudinal fiber web and combine them again with each other in an orientation rotated over 90° (or another suitable angle). It is also possible to make a cross fiber web by attaching pieces of longitudinal fiber web rotated over an angle of 90° (or another suitable angle) to a longitudinal fiber web.
Such webs have properties making them particularly suitable as material for manufacturing for example airbags, bullet proof vests, so called “big bags”, geotextile, primary backing for carpets, thermally deformable plates, etc. Those properties relate to a combination of inter alia large tensile strength and large flexibility. The strength is provided by the fibers, whereas the primary function of the carrier matrix is supplying a manageable product.
A first specific aspect of the present invention relates to providing the fibers which form the starting point for the said fiber bundle. It is common that these fibers are manufactured by a fiber producer, typically by means of an extrusion process, wherein the fiber formed is wound on a fiber reel. The fiber manufacturer supplies fiber reels to the fiber web manufacturer as stock rolls. For the manufacturing process of a fiber web, the fiber web manufacturer mounts a large number of such stock rolls on a yarn rack.
Some disadvantages are associated with this common method. The necessary steps of winding on reels, transport of the reels, and storage of the reels are considered disadvantages which also involve a cost problem. Moreover, the length of the fiber on a reel is not infinite, and an empty reel will have to be replaced while the production of the fiber web continues. During the time required for replacing a fiber reel, a fiber is thus missing in the web formed, which implies a weaker spot; this problem is all the larger as multiple fiber reels become empty at the same time, and the web parts concerned may be considered as waste. Alternatively, one usually chooses to replace all reels at the same time, also the reels that are not yet empty, which thus means that the fibers remaining on those reels are considered as waste. Further, it is then a problem that it is difficult to connect the web parts without variations in the properties: usually, the consequence is that the webs formed have a finite length.
Thus, it is necessary to make sure that becoming empty of the fiber reels is detected as soon as possible, for example by continuous supervision by personnel and/or special detection apparatus.